The invention relates to catalysts, reactors and methods of producing hydrogen from the water gas shift reaction.
Hydrogen gas (H2) can be readily produced from synthesis gas (syngas) by steam reforming, or partial oxidation, or autothermal reforming of hydrocarbons. Additional H2 is then produced by allowing syngas to react with steam according to the following exothermic water gas shift reaction (WGSR):
CO+H2Oxe2x95x90H2+CO2 
The thermodynamics of WGSR are well known. The equilibrium constant of this reaction increases as temperature deceases. Hence, to increase the production of H2, it is desirable to conduct the reaction at lower temperatures, which are also preferred from the standpoint of steam economy.
Two types of commercially available WGSR catalysts are: iron-based high temperature (HT) shift and copper-based low temperature (LT) shift catalysts with Cu based catalysts being relatively more active. However, both catalysts are not very active under their applicable conditions as indicated by their operational contact times (contact time is defined as catalyst bed volume divided by volumetric gas feed flowrate at standard temperature and pressure) of several seconds. Longer contact times imply the requirement of large catalyst bed volume. Operating at shorter contact times with these commercial catalysts requires higher reaction temperatures, which not only accelerates catalyst deactivation due to metal sintering but also disfavors the thermodynamics of the WGSR, as mentioned above.
It has been discovered that the use of a zirconia-supported, alkali-metal-modified, ruthenium catalyst in the water gas shift reaction produces unexpectedly superior results.
In one aspect, the invention provides a catalyst comprising: a porous substrate having an average pore size of from 1 xcexcm to 1000 xcexcm, and, disposed over the porous substrate, a zirconia-supported, alkali-metal-modified, ruthenium catalyst.
The catalyst can be made by wash-coating zirconia-supported alkali-metal-modified ruthenium catalyst on a porous substrate. Zirconia supported alkali-metal modified ruthenium catalyst can be prepared, for example, using the incipient wetness method.
In a related aspect, the invention provides a new method of producing hydrogen gas. In this method, a reactant gas mixture comprising carbon monoxide and water vapor is contacted with the zirconia-supported, alkali-metal-modified, ruthenium catalyst.
The invention also provides a reactor containing the inventive catalyst. Typically, the reactor contains a reactor inlet, a reaction chamber, and a reactor outlet. It is particularly advantageous for the reactor to also contain a microchannel heat exchanger in thermal contact with the reaction chamber. The microchannel heat exchanger enables rapid heat transfer from the reaction chamber thus allowing the inventive catalyst to operate at near isothermal and low temperature conditions to maximize CO2 selectivity while maintaining high conversions of carbon monoxide.
Another related aspect of the present invention is the use of the catalyst in a hydrogen production system. For example, the invention includes a fuel system containing the above-described reactor. In another aspect, the invention provides a hydrogen production system having a fuel source (preferably a liquid fuel tank); a primary conversion reactor (where a process such as steam reforming, partial oxidation, or autothermal reforming is conducted) to produce a gas mixture containing hydrogen, carbon dioxide, and carbon monoxide; and a water gas shift reactor. The water gas shift reactor includes a shift reactor inlet, a reaction chamber, and a shift reactor outlet. The shift reactor inlet is connected to the primary conversion reactor exhaust outlet such that carbon-monoxide-containing exhaust from the primary conversion reactor is fed into the shift reactor. The reaction chamber contains a zirconia-supported, alkali-metal-modified, ruthenium catalyst.
Various embodiments of the invention can provide numerous advantages including one or more of the following: high carbon monoxide conversions, high carbon dioxide selectivity, low methane selectivity, operation at short contact times, and low temperature operation.
The subject matter of the present invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. However, both the organization and method of operation, together with further advantages and objects thereof, may best be understood by reference to the following description taken in connection with accompanying drawings wherein like reference characters refer to like elements.